The flash point of a substance is used in connection with transport and safety regulations in order to define flammable and explosive materials. The flash point can also give information about the presence of readily volatile and flammable components in substances of low volatility and flammability.
Several internationally recognized measuring methods, recognized by ASTM and ISO, exist for measuring the flash point. The definition of flash point according to ASTM is the point of lowest temperature, corrected to the barometric air pressure of 101.3 kPa at which through application of a test flame the vapor of the sample ignites. Igniting is defined as a flame which by itself wanders over the surface of the sample and covers at least two thirds of the surface.
In principle, these methods always involve a sample vessel which is heated with a flame or electrically. The vessel is either open or closed. The open design is rarely still permitted for test measurements since the volatile components give off vapors and can no longer contribute to the combustion.
All test arrangements with closed vessels have in common the method of heating the vessel from the vessel. Thereby the temperature of the cover always lags behind so that condensation phenomena and flash point increases connected therewith occur.
Ignition of the mixture takes place by dipping an ignition flame, an incandescent filament or an electric spark into an opening of the cover.
From DDR-P 124 682 it is known to irradiate a sample vessel in a chamber with a floor, wall, and ceiling heating system wherein to avoid local overheating of the vessel, the three heating groups are appropriately power-controlled. Such power regulations are problematic and the measurement itself is complicated.
Reference is also made to my U.S. Pat. No. 4,901,559, hereby incorporated by reference, which is directed to a method for measuring vapor pressure of liquids in a previously-evacuated measuring cell, and influence of the gas dissolved in the liquid on the measuring results is eliminated.
The detection of a flash point takes place either manually through optical observation through the ignition opening or automatically via temperature measurements (temperature rise due to combustion) or an ionization measurement (changes of the ionization state of the gas due to combustion). The disadvantage of this detection in the case of manual observation is the subjective judgement of the flame size. Automatic detection through heat or ionization provides poor reproducibility since the flame size can rarely be determined.